The invention concerns the ventilating system for a vehicle cab, in particular for the cab of an agricultural or industrial vehicle.
U.S. Pat. No. 4,319,519 shows a ventilating system of the aforementioned type in which a box-shaped filter housing can be exchanged for the evaporator of a cooling system. This ventilating system is obviously intended for passenger vehicles.
In agricultural or industrial vehicles, such as agricultural tractors, it is desirable for the conditioning of the air in the cab not only to draw in fresh air from the outside, but also to recirculate the air inside the cab. This permits the service interval to be lengthened, since the filters for the outside air do not become dirty as rapidly, and the power requirement for temperature equalization in the cab can be reduced. For example, EP-A-0 042 597 describes an air distribution arrangement with two blowers, of which a first blower, located downstream of a fresh air filter, draws fresh air from the outside into the operator's cab and a second blower, located downstream of a recirculating air filter, recirculates only interior air. The outside air drawn in by the blower and the interior air are combined in a mixing zone that is downstream of both blowers. Each filter can be removed separately for cleaning or replacement. This is relatively costly and an operator may forget to clean the recirculating air filter.
EP-B-0 070 636 describes a heating and ventilating system for a tractor cab, which includes only a fresh air circuit. The fresh air circuit contains a filter which is accessible from an opening above, in the roof region of the tractor. The filter can be inserted or removed from the fresh air flow through this opening. Recirculation of the air in the cab is not described.
DE-C-36 43 478 shows an air filter box for an operator's cab, in which the air flows through a filter unit arranged in a roof region projecting beyond the side wall of the cab. The filter unit consists of a filter box that accommodates a filter and is suspended so as to pivot, so that it can be swung downward for the removal and cleaning of the filter. Here too, there is no reference to recirculation of the air in the cab.